Back to EveryPatent.com
United States Patent |
5,262,819
|
Ohtaka
,   et al.
|
November 16, 1993
|
Compact focus detecting device suitable for incorporation into an
optical apparatus
Abstract
A compact focus detecting device featuring increased optical paths includes
a first detecting system having first light intensity distribution forming
structure for forming a light beam passing through the objective lens a
light intensity distribution of which varies in relative position
according to the focus state of the objective lens. A first light
receiving sensor receives the first light intensity distribution and
outputs a first signal indicative of the focused state of the objective
lens. The first detecting system has a first detection field and a first
optical path. A second detecting system has a second detecting field with
a center spaced apart from the center of the first detection field, and a
second optical path. The second detecting system includes second light
intensity distribution forming structure for forming from the light beam
passing through the objective lens a light intensity distribution which
varies in relative position according to the focused state of the
objective lens. A second light receiving sensor receives the second light
intensity distribution and outputs a second signal indicative of the focus
state of the objective lens. A light transmitting optical member is
provided for adjusting the length of the first and second optical paths.
Preferably, the optical member comprises a block having an internal
reflecting surface.
Inventors:
|
Ohtaka; Keiji (Yokohama, JP);
Koyama; Takeshi (Yokohama, JP);
Suda; Yasuo (Yokohama, JP)
|
Assignee:
|
Canon Kabushiki Kaisha (Tokyo, JP)
|
Appl. No.:
|
824873 |
Filed:
|
January 22, 1992 |
Foreign Application Priority Data
| Jul 07, 1989[JP] | 1-176467 |
| Jul 07, 1989[JP] | 1-176468 |
| Jul 07, 1989[JP] | 1-176469 |
Current U.S. Class: |
396/114 |
Intern'l Class: |
G03B 013/00 |
Field of Search: |
354/402,406-408
|
References Cited
U.S. Patent Documents
4774539 | Sep., 1988 | Suda et al. | 354/406.
|
4841326 | Jun., 1989 | Koyama et al. | 354/406.
|
4859842 | Aug., 1989 | Suda et al. | 354/408.
|
4878078 | Nov., 1989 | Koyama et al. | 354/402.
|
4901102 | Feb., 1990 | Karasaki et al. | 354/408.
|
4908504 | Mar., 1990 | Karasaki et al. | 354/408.
|
4954701 | Sep., 1990 | Suzuki et al. | 354/406.
|
4959677 | Sep., 1990 | Suda et al. | 354/402.
|
4992819 | Feb., 1991 | Ohtaka et al. | 354/408.
|
5109154 | Apr., 1992 | Higashihara et al. | 354/407.
|
Foreign Patent Documents |
59-107311 | Jun., 1984 | JP.
| |
59-107313 | Jun., 1984 | JP.
| |
62279835 | May., 1989 | JP.
| |
63274940 | May., 1990 | JP.
| |
Primary Examiner: Gray; David M.
Attorney, Agent or Firm: Fitzpatrick, Cella, Harper & Scinto
Parent Case Text
This application is a continuation of application Ser. No. 07/548,849 filed
Jul. 6, 1990, now abandoned.
Claims
We claim:
1. A device for detecting the focus adjusted state of an objective lens,
comprising:
a first detecting system including first light intensity distribution
forming means for forming from a light beam passing through the objective
lens a light intensity distribution varying in relative position in
conformity with a focus adjusted state of the objective lens, and first
light receiving means responsive to the light intensity distribution to
output a first signal indicative of the focus adjusted state and having a
plurality of photosensors, said first detecting system having a first
detection field and a first optical path;
a second detecting system having a second detection field having a center
spaced apart from a center of said first detection field and a second
optical path, said second detecting system including second light
intensity distribution forming means for forming from the light beam
passing through the objective lens a light intensity distribution varying
in relative position in conformity with the focus adjusted state of the
objective lens, and second light receiving means responsive to the light
intensity distribution to output a second signal indicative of the focus
adjusted state and having a plurality of photosensors; and
a light transmitting optical member for adjusting the lengths of said first
and second optical paths, said optical member comprising a block having an
internal reflecting surface.
2. A device according to claim 1, wherein said first and second light
intensity distribution forming means each have a pair of secondary imaging
lenses, and the respective optical member is disposed between said
secondary imaging lenses and said first and second light receiving means.
3. A device according to claim 2, wherein said secondary imaging lenses are
coupled to said optical member.
4. A device according to claim 1, wherein said optical member comprises
polycarbonate resin.
5. A device according to claim 1, wherein said optical member comprises
polystyrene resin.
6. A device according to claim 1, wherein said optical member comprises
optical glass.
7. A device according to claim 1, further comprising:
a third detecting system having a third detection field having a center
spaced apart from the centers of said first and second detection fields,
and a third optical path passing through said optical member, said third
detecting system including third light intensity distribution forming
means for forming from the light beam passing through the objective lens a
light intensity distribution varying in relative position in conformity
with the focus adjusted state of the objective lens, and third light
receiving means responsive to the light intensity distribution to output a
third signal indicative of the focus adjusted state and having a plurality
of photosensors.
8. A device according to claim 7, wherein said first, second and third
light receiving means are formed on a single substrate.
9. A device according to claim 1, wherein said first detecting system
comprises two sub-detecting systems having sub-detection fields
intersecting each other.
10. Apparatus for detecting the focus state of an objective lens,
comprising:
a first detecting system including first light intensity distribution
forming means for forming from a light beam passing through the objective
lens a first light intensity distribution which varies in relative
position in accordance with the focus state of the objective lens, and
first light receiving means responsive to the first light intensity
distribution for outputting a first signal indicative of the focus
adjusted state of the objective lens, said first detecting system having a
first detection field and a first optical path;
a second detecting system including a second light intensity distribution
forming means for forming from a light beam passing through the objective
lens a second light intensity distribution which varies in relative
position in accordance with the focus state of the objective lens, and
second light receiving means responsive to the second light intensity
distribution for outputting a second signal indicative of the focus
adjusted state of the objective lens, said second detecting system
including a second detection field having a center which is spaced apart
from a center of said first detection field, and a second optical path;
a light transmitting optical member for adjusting the lengths of said first
and second optical paths; and
first and second reflection planes provided in an optical path which is
defined by connecting said first and second light intensity distribution
forming means and a prospective focusing plane of the objective lens, an
optical path of a light beam directed toward said first reflection plane
and the optical path of a light beam projected away from said second
reflection plane crossing each other.
11. Apparatus according to claim 10, wherein said optical member comprises
a single block having an internal reflection plane.
12. A device for detecting the focus adjusted state of an objective lens,
comprising:
a first detecting system including first light intensity distribution
forming means for forming from a light beam passing through the objective
lens a first light intensity distribution varying in relative position in
conformity with a focus adjusted state of the objective lens, and first
light receiving means responsive to the first light intensity distribution
to output a first signal indicative of the focus adjusted state and having
a plurality of photosensors, said first detecting system having a first
detection field; and
a second detecting system having a second detection field partially
overlapping with said first detection field, said second detecting system
including second light intensity distribution forming means for forming
from the light beam passing through the objective lens a second light
intensity distribution varying in relative position in conformity with the
focus adjusted state of the objective lens, and second light receiving
means responsive to the second light intensity distribution to output a
second signal indicative of the focus adjusted state and having a
plurality of photosensors, wherein
said first light intensity distribution forming means includes a set of
first apertures, said second light intensity distribution forming means
includes a set of second apertures, said first and second sets of
apertures each partially border a hypothetical circumscribing circle, and
an optical characteristic of said first apertures being different from
that of said second apertures.
13. A device according to claim 12, wherein at least one of opening area,
distance between centers of openings, and width of opening is different
between the first set of apertures and the second set of apertures.
14. A device for detecting the focus adjusted state of an objective lens,
comprising:
a first detecting system including first secondary imaging lens means for
forming form a light beam passing through the objective lens a first light
intensity distribution varying in relative position in conformity with a
focus adjusted state of the objective lens, and first light receiving
means responsive to the first light intensity distribution to output a
first signal indicative of the focus adjusted state and having a plurality
of photosensors, said first detecting system having a first detection
field;
a second detecting system having a second detection field having a center
spaced apart from a center of said first detection field, said second
detecting system including second secondary imaging lens means for forming
from the light beam passing through the objective lens a second light
intensity distribution varying in relative position in conformity with the
focus adjusted state of the objective lens, and second light receiving
means responsive to the second light intensity distribution to output a
second signal indicative of the focus adjusted state and having a
plurality of photosensors;
a reflection surface, located on a light path between said first and second
secondary imaging lens means and said first and second light receiving
means, for reflecting said first and second light intensity distributions
to said first and second light receiving means, respectively; and
an optical transmission substance interposed between said reflection
surface and said first and second secondary imaging lens means.
15. A device for detecting the focus adjusted state of an objective lens,
comprising:
a first detecting system including first secondary imaging lens means for
forming from a light beam passing through the objective lens a first light
intensity distribution varying in relative position in conformity with a
focus adjusted state of the objective lens, and first light receiving
means responsive to the first light intensity distribution to output a
first signal indicative of the focus adjusted state and having a plurality
of photosensors, said first detecting system having a first detection
field;
a second detecting system having a second detection field having a center
spaced apart from a center of said first detection field, said second
detecting system including second secondary imaging lens means for forming
from the light beam passing through the objective lens a second light
intensity distribution varying in relative position in conformity with the
focus adjusted state of the objective lens, and second light receiving
means responsive to the second light intensity distribution to output a
second signal indicative of the focus adjusted state and having a
plurality of photosensors;
a reflection surface, located on a light path between said first and second
secondary imaging and said first and second light receiving means, for
reflecting said first and second light intensity distributions to said
first and second light receiving means, respectively; and
an optical transmission substance interposed between said reflection
surface and said first and second light receiving means.
16. A device for detecting the focus adjusted state of an objective lens,
comprising:
a first detecting system including first secondary imaging lens means for
forming from a light beam passing through the objective lens a first light
intensity distribution varying in relative position in conformity with a
focus adjusted state of the objective lens, and first light receiving
means responsive to the first light intensity distribution to output a
first signal indicative of the focus adjusted state and having a plurality
of photosensors, said first detecting system having a first detecting
field;
a second detecting system having a second detection field having a center
spaced apart from a center of said first detection field, said second
detecting system including second secondary imaging lens means for forming
from the light beam passing through the objective lens a second light
intensity distribution varying in relative position in conformity with the
focus adjusted state of the objective lens, and second light receiving
means responsive to the second light intensity distribution to output a
second signal indicative of the focus adjusted state and having a
plurality of photosensors; and
a prism of triangular cross-section having an inclined reflection surface
and being located adjacent to or connected to said first and second
secondary imaging lens means.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a focus detecting device suitable for a
photographic camera, a video camera or the like, and in particular to a
focus detecting device suitable for dividing the pupil of an objective
lens into a plurality of areas, forming light intensity distributions
regarding a plurality of object images by the use of light beams passing
through said areas, and finding the relative positional relation between
the plurality of light intensity distributions to thereby detect the
in-focus state of the objective lens.
2. Related Background Art
As a passive type focus detecting system utilizing a light beam passing
through an objective lens, there is the so-called correlation system.
This correlation system is well known, for example, from Japanese Laid-Open
Patent Application No. 59-107311, Japanese Laid-Open Patent Application
No. 59-107313, etc.
FIG. 13 of the accompanying drawings is a schematic view of the optical
system of a focus detecting device using the prior-art correlation system.
In FIG. 13, the reference numeral 61 designates an objective lens, and the
reference numeral 62 denotes a field mask disposed near the predetermined
imaging plane of the objective lens 61. The reference numeral 63
designates a field lens disposed near the predetermined imaging plane. The
reference numeral 64 denotes a secondary optical system comprised of two
lenses 64-1 and 64-2 disposed symmetrically with respect to the optic axis
of the objective lens 61. The reference numeral 65 designates light
receiving means having two light receiving element arrays 65-1 and 65-2
disposed rearwardly of the two lenses 64-1 and 64-2 correspondingly
thereto. The reference numeral 66 denotes a stop having two opening
portions 66-1 and 66-2 disposed rearwardly of the two lenses 64-1 and 64-2
correspondingly thereto. The reference numeral 67 designates the exit
pupil of the objective lens 61 which is comprised of two divided areas
67-1 and 67-2.
The field lens 63 has the function of imaging the opening portions 66-1 and
66-2 on the areas 67-1 and 67-2, respectively, of the exit pupil 67, and
light beams passed through the areas 67-1 and 67-2 may form light
intensity distributions on the light receiving element arrays 65-1 and
65-2, respectively. It is to be understood that the light includes not
only visible light but also invisible light.
In the focus detecting device shown in FIG. 13, where the imaging point of
the objective lens 61 is forward of the predetermined imaging plane, the
light intensity distributions regarding the object images formed on the
two light receiving element arrays 65-1 and 65-2, respectively, become
close to each other, and where the imaging point of the objective lens 61
is rearward of the predetermined imaging plane, the light intensity
distributions formed on the two light receiving element arrays 65-1 and
65-2, respectively, become far from each other. Moreover, the amount of
deviation between the light intensity distributions formed on the two
light receiving element arrays 65-1 and 65-2, respectively, is in a
certain functional relation with the amount of out-of-focus of the
objective lens 61 and therefore, if that amount of deviation is calculated
by suitable calculating means, the direction and amount of out-of-focus of
the objective lens 61 can be detected.
The focus detecting device shown in FIG. 13 is effecting distance
measurement for an object existing substantially centrally of the object
range photographed by the objective lens.
In contrast, a focus detecting device capable of accomplishing focus
detection with respect to any other measuring point than the central
portion of the photographing range has previously been proposed by the
applicant in Japanese Patent Application No. 62-279835.
FIG. 14 of the accompanying drawings is a schematic view of the optical
system of a focus detecting device for a plurality of distance measuring
points proposed in Japanese Patent Application No. 62-279835. In FIG. 14,
the reference numeral 71 designates a field mask, the reference numeral 72
denotes a field lens, the reference numeral 73 designates a stop having
two openings 73-1 and 73-2, the reference numeral 74 denotes a secondary
optical system comprising two lenses 74-1 and 74-2, and the reference
numeral 75 designates a sensor. The objective lens 61 shown in FIG. 13 is
not shown in FIG. 14.
In FIG. 14, the field mask 71 has a plurality of openings 71a-71e
correspondingly to a plurality of fields of view to be focus-detected, and
pairs of sensor arrays 75a1 and 75a2, 75b1 and 75b2, 75c1 and 75c2, 75d1
and 75d2, and 75e1 and 75e2 are provided as the sensor unit 75 so as to
receive pairs of light intensity distributions which the light beams
controlled by the field mask 71 form by the secondary optical system 74.
In FIG. 14, detection is effected in five areas, i.e., the central portion
of the photographing picture plane and four locations on both sides
thereof. It is very important for applying the focus detecting device to a
camera that focus detection can be effected in a plurality of areas in the
photographing picture plane by such a simple construction.
In the focus detecting device shown in FIG. 14, depending on the focus
state of the objective lens, the direction in which the two light
intensity distributions on the sensor move relative to each other is a
vertical direction and therefore, detection is possible only for an object
having a variation in the light intensity distribution in this direction,
and accuracy of distance measurement may be reduced for an object having a
variation in the light intensity distribution only in a direction
perpendicular to said direction, such as, for example, a black and white
edge pattern with a vertical line as a boundary.
Therefore, the applicant has proposed in Japanese Patent Application No.
63-274940 a focus detecting device which can accomplish distance
measurement even for an object whose light intensity distribution varies
only in one direction, i.e., a vertical or horizontal direction, near the
center of the photographing range and moreover, can accomplish detection
even at a plurality of other points than the vicinity of the center of the
photographing range.
FIG. 15 of the accompanying drawings shows the essential portions of the
focus detecting device proposed in Japanese Patent Application No.
63-274940.
In FIG. 15, the reference numeral 31 designates a field mask having, for
example, a cruciform opening 31-1 intersecting substantially at the center
of the photographing picture plane of an objective lens (a photo-taking
lens), not shown, and vertically long openings 31-2 and 31-3 on both sides
of the cruciform opening 31-1. The reference numeral 32 denotes a field
lens comprising three areas 32-1, 32-2 and 32-3 each having a
predetermined optical characteristic correspondingly to the three openings
31-1, 31-2 and 31-3 in the field mask 31. The reference numeral 33
designates a stop having a vertical pair of openings 33-1a and 33-1b and a
horizontal pair of openings 33-1c and 33-1d in the central portion
thereof, and two pairs of openings 33-2a and 33-2b, 33-3a and 33-3b in the
marginal portion thereof. The areas 32-1, 32-2 and 32-3 of the field lens
32 have the function of imaging the openings 33-1, 33-2 and 33-3 in the
stop 33 which form respective pairs near the exit pupil of the
photo-taking lens not shown. The reference numeral 34 denotes a secondary
optical system which, as a whole, has four pairs of secondary imaging
lenses. That is, the secondary optical system 34 as a whole comprises
eight secondary imaging lenses 34-1a, 34-1b, 34-1c, 34-1d, 34-2a, 34-2b,
34-3a and 34-3b disposed rearwardly of the openings in the stop 33
correspondingly thereto.
The reference numeral 35 designates a light receiving element unit (a
sensor unit) which, as a whole, has four pairs of sensor arrays. That is,
the light receiving element unit 35 as a whole comprises eight sensor
arrays 35-1a, 35-1b, 35-1c, 35-1d, 35-2a, 35-2b, 35-3a and 35-3b disposed
correspondingly to the secondary imaging lenses so as to receive the
images formed thereby.
FIG. 16 of the accompanying drawings illustrates image areas formed on the
surface of the sensor 35 of FIG. 15. Areas 36-1a, 36-1b, 36-1c and 36-1d
are the image areas of the central opening 31-1 in the field mask 31, and
show a state in which a light beam transmitted through the central portion
32-1 of the field lens 32 is controlled by the openings 33-1a, 33-1b,
33-1c and 33-1d, and thereafter is formed on the surface of the sensor 35
by the secondary imaging lenses 34-1a, 34-1b, 34-1c and 34-1d rearward of
said openings. The reference characters 36-2a and 36-2b denote the image
areas of the opening 31-2 in the marginal portion of the field mask 31,
and these image areas show a state in which a light beam transmitted
through the marginal portion 32-2 of the field lens 32 is controlled by
the openings 33-2a and 33-2b in the stop 33, and thereafter is fomred on
the sensor unit 35 by the secondary imaging lenses 34-2a and 34-2b
rearward of said openings. Likewise, openings 36-3a and 36-3b are the
image areas of the opening 31-3 in the marginal portion of the field mask
31, and show image areas in which a light beam transmitted through the
marginal portion 32-3 of the field lens 32 is controlled by the openings
33-3a and 33-3b in the stop 33, and thereafter is formed on the surface of
the sensor 35 by the secondary imaging lenses 34-3a and 34-3b rearward of
said openings.
The focus detecting device shown in FIG. 15 is designed such that focus
detection can be accomplished in the center of the field of view in the
photographing range as well as in the other areas than the center of the
field of view, and this has led to the tendency that the secondary optical
system, the light receiving means, etc. become relatively bulky due to the
relation with the length of the optical path leading from the secondary
optical system to the light receiving means.
Also, it is desirable from the point of detection accuracy to set the
imaging magnification of the secondary optical system to a suitable value
(e.g. about 1/3 time), but according to this, the position at which the
secondary optical system is disposed is determined almost primarily by the
full length of the focus detecting system and therefore, the degree of
freedom of the arrangement of the various optical elements has been
limited.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a focus detecting
device capable of accomplishing highly accurate focus detection in which
various optical elements from a secondary imaging optical system to a
light receiving unit are appropriately set, whereby the detection in a
plurality of areas in the photographing range is made possible and yet the
compactness of the entire device is achieved and there are few limitations
in the degree of freedom of assemblage and further the optimization of the
imaging magnification of the secondary imaging optical system is made
easy.
It is also an object of the present invention to provide a focus detecting
device in which when the luminance of an object to be photographed is low
and focus detection becomes difficult by only natural light (outdoor
light), a pattern of a predetermined shape is projected toward the object
to be photographed from an auxiliary illuminating system provided in a
camera body or a stroboscopic lamp to thereby form a pattern on the
surface of the object to be photographed and the light intensity
distribution of the image of said pattern is detected, whereby for objects
of any luminance, highly accurate focus detection can be accomplished at a
plurality of points in the photographing range.
It is a further object of the present invention to provide a device in
which at least first and second focus detecting systems are disposed
rearwardly of the predetermined imaging plane of an objective lens, said
focus detecting systems each having a secondary optical system for forming
a plurality of light intensity distributions regarding an object image by
the use of light beams passed through different areas of said objective
lens when the in-focus state of said objective lens is to be found by the
utilization of said focus detecting systems, a stop for limiting the
quantity of light entering said secondary optical system, and light
receiving means for detecting the relative positional relation between the
respective light intensity distributions, said first and second focus
detecting systems differing from each other in the auxiliary illumination.
This allows a central portion of the detection field of view in the light
intensity distribution area of the object image to be detected, the
optical path from the lens surface of said secondary optical system to
said light receiving means being filled with an optical member formed of a
transparent medium having a refractive index higher than that of air.
Said optical member comprises a prism having a reflecting surface for
deflecting a light beam incident from the first lens surface of said
secondary optical system, said reflecting surface reflecting the incident
light in a direction substantially perpendicular to a segment linking the
center points of the stops of said first and second focus detecting
systems.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a perspective view showing the essential portions of an optical
system according to an embodiment of the present invention.
FIG. 2 is an optical cross-sectional view of the present invention as it is
applied to a single-lens reflex camera.
FIGS. 3 to 7A, 7B and 7C illustrate various elements according to an
embodiment of the present invention.
FIGS. 8A, 8B and 8C show stop openings.
FIGS. 9 and 10 show projected patterns.
FIGS. 11A and 11B show optical arrangements supposed to make the effect of
the embodiment readily understood.
FIG. 12 shows stop openings for comparison with the present embodiment.
FIGS. 13 and 14 are perspective views of the devices according to the prior
art.
FIG. 15 is a perspective view of the related art.
FIG. 16 is a front view of the sensor unit of FIG. 15.
FIG. 17 is a front view of the secondary imaging lens.
FIG. 18 shows a projected image of the secondary imaging lens onto the
sensor.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
FIG. 1 schematically shows the essential portions of an optical system
according to an embodiment of the present invention, and FIG. 2
schematically shows the essential portions of an embodiment when the focus
detecting device of the present invention shown in FIG. 1 is applied to a
single-lens reflex camera.
The present embodiment differs greatly from the prior-art focus detecting
device shown in FIG. 12 in optical elements in the optical path leading
from a secondary optical system to light receiving means (sensor).
A description will now be given of the construction of the focus detecting
system shown in FIG. 1.
In FIG. 1, the reference numeral 31 designates a field mask having, for
example, a Grecian cruciform opening 31-1 intersecting substantially at
the center of the photographing picture plane provided by the objective
lens (photo-taking lens) 37 of FIG. 2 and vertically long openings 31-2
and 31-3 in the marginal portion of the field mask on both sides of the
opening 31-1. The reference numeral 32 denotes a field lens comprising
three areas 32-1, 32-2 and 32-3 each having a predetermined optical
characteristic disposed correspondingly to the three openings 31-1, 31-2
and 31-3 in the field mask 31. The reference numeral 33 designates a stop
having in the central portion thereof a vertical pair of openings 33-1a
and 33-1b and a horizontal pair of openings 33-1c and 33-1d which are
inscribed to a substantially circular area 52-1, and two pairs of openings
33-2a and 33-2b and 33-3a and 33-3b formed in the right and left marginal
portions of the stop and inscribed to substantially circular areas 52-2
and 52-3, respectively. The areas 32-1, 32-2 and 32-3 of the field lens 32
have the function of imaging the pairs of openings 33-1, 33-2, 33-3 in the
stop near the exit pupil of the photo-taking lens 37 of FIG. 2. The
reference numeral 34 denotes a secondary optical system which as a whole
has four pairs of secondary imaging lenses. That is, the secondary optical
system 34 as a whole comprises eight secondary imaging lenses 34-1a,
34-1b, 34-1c, 34-1d, 34-2a, 34-2b, 34-3a and 34-3b disposed rearwardly of
the respective openings in the stop 33 correspondingly thereto.
The reference numeral 49 designates an optical member formed, for example,
of polycarbonate resin or polystyrene resin which is a transparent medium,
or glass or the like. The optical path leading from the secondary optical
system 34 to a light receiving unit 35 which will be described is filled
with the optical member 49 to adjust the length of the optical path. In
FIG. 2, as will be described later, the optical member 49 is comprised of
a prism having a reflecting surface.
The reference numeral 35 denotes a light receiving unit (a sensor unit)
comprising a single substrate. The light receiving unit 35 as a whole has
four pairs of sensor arrays. That is, the light receiving unit 35 as a
whole comprises eight sensor arrays 35-1a, 35-1b, 35-1c, 35-1d, 35-2a,
35-2b, 35-3a and 35-3b disposed correspondingly to the secondary imaging
lenses so as to receive the light intensity distributions regarding the
images thereof.
In the present embodiment, the elements 31-1, 32-1, 33-1a, 33-1b, 34-1a,
34-1b, 35-1a and 35-1b together constitute a first focus detecting system,
the elements 31-2, 32-2, 33-2a, 33-2b, 34-2a, 34-2b, 35-2a and 35-2b
together constitute a second focus detecting system, and the elements
31-3, 32-3, 33-3a, 33-3b, 34-3a, 34-3b, 35-3a and 35-3b together
constitute a third focus detecting system.
The distance measuring principle of the focus detecting device of the
present invention shown in FIG. 1, like the conventional so-called
correlation system, is based on detecting the relative position of the
images in the direction of array of the sensors forming a pair.
In the present embodiment, the construction as described above is adopted,
whereby near the center of the photographing range photographed or
observed by means of the objective lens 37 of FIG. 2, detection becomes
possible even for an object whose light intensity distribution varies only
in one of the vertical and horizontal directions, and detection can
likewise be accomplished for objects lying at any other positions than the
center, for example, positions spaced apart from each other about the
center.
A description will now be given of various elements when the present
invention of FIG. 1 is applied to a single-lens reflex camera.
In FIG. 2, the reference numeral 37 designates a fixed or removably mounted
photo-taking lens (objective lens), the reference numeral 38 denotes a
quick return mirror, the reference numeral 39 designates a focusing
screen, the reference numeral 40 denotes a pentaprism, the reference
numeral 41 designates an eyepiece, the reference numeral 42 denotes a film
surface, and the reference numeral 43 designates a sub-mirror secured to a
portion of the quick return mirror 38. The reference numeral 31 denotes a
field mask disposed at a position substantially optically equivalent to
the film surface 42. The reference numeral 44 designates an infrared cut
filter disposed rearwardly of the field mask 31. The reference numeral 32
denotes a field lens, the reference numerals 45 and 46 designate first and
second total reflection mirrors, respectively, the reference numeral 47
denotes a light-intercepting mask, the reference numeral 33 designates a
stop, and the reference numeral 34 denotes a secondary optical system
formed integrally with an optical member 49 comprising a prism which will
be described later. The optical member 49 comprising the prism of FIG. 2
as is developed below corresponds to the optical member 49 of FIG. 1. The
reference numeral 35 designates a sensor unit having cover glass 50-1 and
a light receiving surface 50-2.
In the present embodiment, the field mask 31 to the sensor unit 35
correspond to the focus detecting device shown in FIG. 1.
In FIG. 2, the optical path of the focus detecting optical system is bent
by the use of three reflecting surfaces 45, 46 and 49-1, whereby the full
length of the focus detecting optical system, particularly the spacing
between the field lens 32 and the stop 33, is kept long. As previously
described, the field lens 32 has the function of imaging the stop 33 near
the exit pupil of the photo-taking lens 37, and by lengthening the spacing
between the field lens 32 and the stop 33, it becomes possible to keep
this imaging relation good and a brighter light beam can be directed to
the focus detecting device. Also, in FIG. 2, the reference numeral 101
designates a light projection lens, and the reference numeral 102 denotes
a pattern plate which projects a pattern as shown in FIG. 9 when the
object to be photographed is dark or is low in contrast.
The features of the various elements shown in FIGS. 1 and 2 will now be
described.
FIG. 3 is a view of the field lens as it is individually taken. This figure
shows a cross-sectional shape taken along a plane containing the optic
axis of the field lens 32 shown in FIG. 2 and perpendicular to the plane
of the drawing sheet. The field lens comprises three areas 32-1, 32-2 and
32-3 disposed correspondingly to the three openings 31-1, 31-2 and 31-3 in
the field mask 31, and the optic axes 51-2 and 51-3 of the lenses 32-2 and
32-3, respectively, forming the marginal areas which lie at positions
deviating from the center 51-1. It is effective to make each lens surface
of the field lens 32 aspherical to enhance the performance of the field
lens 32. Particularly, by at least one of the two surfaces of each of the
marginal lens portions 32-2 and 32-3 being formed by an aspherical
surface, the quantity of light entering the focus detecting system from
the marginal field of view can be increased.
FIG. 4 is an illustration showing an embodiment of the shapes of openings
in the stop 33. The central group of openings comprises a vertical pair of
openings 33-1a and 33-1b and a horizontal pair of openings 33-1c and 33-1d
which are inscribed to a substantially circular area 52-1. The right and
left marginal openings comprise a vertical pair of openings 33-2a and
33-2b and a vertical pair of openings 33-3a and 33-3b, respectively, which
are likewise inscribed to substantially circular areas 52-2 and 52-3,
respectively.
In the present embodiment, the openings in the stop 33 are such that the
diameters of the areas 52-2 and 52-3 are set to be smaller than the
diameter of the area 52-1 because the aperture eclipse of the photo-taking
lens 37 is greater in the marginal portion thereof than in the central
portion thereof. The aperture eclipse of the photo-taking lens 37 in the
marginal portion thereof occurs chiefly in the horizontal direction in
FIG. 4 and therefore, it is also possible that the openings in the stop
are formed in vertically long elliptical areas 52'-2 and 52'-3 as shown in
FIG. 5. By doing so, it becomes possible to introduce a greater quantity
of light.
As shown in FIG. 4, the openings in the stop 33 are such that in the
central portion, the upper and lower openings 33-1a and 33-1b are larger
than the right and left openings 33-1c and 33-1d. This is for the
following reasons.
In a camera using a focus detecting device, there is often adopted a system
whereby when the object to be photographed is low in contrast, an
auxiliary light is projected onto the object side, thereby effecting
distance measurement by a pattern projected onto the object. In such case,
it is necessary to project a lateral-striped pattern onto the marginal
field of the photographing picture plane, and the projection of a similar
lateral-striped pattern also onto the central field will make the
construction of the light projection system simpler. Accordingly, in the
central field, making the upper and lower openings larger so that a light
beam becoming capable of distance measurement for lateral stripes may be
more directed will be able to more effectively achieve the purpose of the
auxiliary light which enlarges the low luminance limit. This will be
described later.
FIG. 6 shows the shapes of openings 47-1, 47-2 and 47-3 in the
light-intercepting mask 47 of FIG. 2 as it is individually taken. This
light-intercepting mask 47 serves to prevent undesired light which enters
the marginal opening 31-2 or 31-3 in the field mask 31 of FIG. 1 and does
not pass through the marginal openings 33-2a, 33-2b, 33-3a, 33-3b, etc. in
the stop 33 but is transmitted through the central openings 33-1a, 33-1b,
33-1c, 33-1d, etc. in the stop 33 from reaching the surface of the sensor
35. The undesired light reaches the portion between the openings 47-1 and
47-2 or the openings 47-1 and 47-3 in the light-intercepting mask 41, and
thus is intercepted. The light-intercepting mask 47 need not always be
provided at this position, but may be provided immediately forward of the
second reflecting mirror 46 of FIG. 2, or rearward of the field lens 32,
or forward of the stop 33. If the undesired light cannot be fully
intercepted by a single light intercepting mask, it is also possible to
use a combination of several such masks. Also, instead of providing a
light-intercepting mask immediately forward of the first and second
mirrors 45 and 46, the reflecting surfaces of these mirrors may be
patternized so that the light may be absorbed or transmitted in the other
portions than necessary.
FIG. 7A is a perspective view showing the secondary optical system 34 of
FIG. 2 and the optical member (prism member) 49 comprising a prism. The
secondary optical system 34 comprises four pairs of secondary imaging
lenses 34-1a and 34-1b, 34-1c and 34-1d, 34-2a and 34-2b, and 34-3a and
34-3b of positive refractive power which are convex toward the stop 33,
and is made integral with the prism member 49.
The prism member 49 has a reflecting surface 49-1 formed by film of a metal
such as aluminum being deposited by evaporation, and has the function of
reflecting the light beam from the secondary optical system 34 and
deflecting it to the exit surface 49-21 thereof.
The reflecting film of aluminum or the like is not necessary when the light
beam incident on the reflecting surface 49-1 satisfies the condition of
total reflection. Even when there exists a light beam Which does not
satisfy the condition of total reflection for the reflecting surface 49-1
inclined at 45.degree., it is possible to totally reflect all light beams
by inclining the reflecting surface so as to be more approximate to the
horizontal than 45.degree.. In this case, by inclining the exit surface
49-2 of the prism member 49 and the sensor 35 of FIG. 2 from the
horizontal correspondingly thereto, it is possible to eliminate the
optical influence of the reflecting surface 49-1 being inclined. It is
also effective to form the prism member 49 of glass of high refractive
index or a plastic of high refractive index such as polycarbonate or
polystyrene in order to make the critical angle smaller and facilitate the
total reflection.
If in the present embodiment, the imaging magnification is small in the
focus detecting system of the secondary imaging type, the accuracy of
focus detection will be reduced and therefore, it is desirable to secure
an imaging magnification to a certain degree. However, too great an
imaging magnification would result in the bulkiness of the sensor which in
turn would lead to a disadvantage both in space and cost and therefore, it
can be said to be desirable that at least reduced imaging be adopted.
Assuming that the secondary imaging lens 54 is of a plate-like shape as
shown in FIG. 11A, and that the prism member having a reflecting surface
as in the present embodiment is not provided but the sensor 35 is provided
on the direct extension of the optic axis, the distance from the secondary
imaging lens 54 to the sensor 35 cannot be secured sufficiently, for
example, because of the interference with a mechanical member such as a
mount for mounting the objective lens, not shown, and the imaging
magnification of the secondary imaging lens will unavoidably become
considerably small.
On the other hand, if the secondary imaging lens 54 is of a plate-like
shape as shown in FIG. 11B and the prism member having a reflecting
surface as in the present embodiment is replaced by an ordinary mirror 55,
the length of the optical path from the secondary imaging lens 54 to the
sensor will become long and the imaging magnification of the secondary
imaging lens will tend to become too great.
In contrast, by adopting a construction in which the optical path is filled
with the prism member 49 as in the present embodiment shown in FIG. 2, and
changing the size of the prism member 49, it becomes possible to control
the length of the optical path and an optimum design regarding the
aforedescribed imaging magnification can be readily accomplished in a
limited space.
In FIG. 7, the adjacent lenses of the secondary optical system 34 share a
chord as a border line and are in contact with each other. With such a
construction, the lens diameters can be secured greatly and it becomes
possible to increase the quantity of light. It is advantageous in mold
working to set the diameters of the four secondary imaging lenses 34-1a,
34-1b, 34-1c and 34-1d in the central portion so that they may coincide
with one another at the end points 53-1, 53-2, 53-3 and 53-4 of the chord
common to the outer peripheries of the adjacent lenses. Accordingly, where
the shape of the stop 33 is made unequal in the vertical direction and the
horizontal direction as shown in FIG. 4, the lens diameters in the
vertical direction and the horizontal direction do not always coincide
with each other. Further, the radii of curvature of the lens group 34-1 in
the central portion and the lens group 34-2 or 34-3 in the marginal
portion may be equal to each other or may differ from each other. In some
cases, it is effective to make these radii of curvature different from
each other. For example, the field lens 32 comprises three different areas
as shown in FIG. 3 and therefore, the thickness and the manner in which
the light is deflected differ between the central portion and the marginal
portion and the lengths of the optical paths to the surface of the sensor
35 do not always coincide with each other. So, in the central portion and
the marginal portion of each secondary imaging lens, the radii of
curvature of that lens are made different from each other, whereby it
becomes possible to image well on the surface of the same sensor 35.
Particularly, the light beam from the marginal portion follows an optical
path somewhat inclined toward the center and thus, generally, the length
of the optical path of the marginal light beam to the surface of the
sensor 35 is longer than that of the central light beam and therefore, it
is effective to make the radii of curvature of the marginal secondary
imaging lenses 34-2 and 34-3 somewhat larger than that of the central
secondary imaging lens. Also, if the spacing between the secondary optical
system 34 and the stop 33 becomes wider, it will be necessary to make each
opening in the stop 33 small in order that the light beam may not reach
the vicinity of the border line between the divided lenses, and it will
become difficult to secure a sufficient quantity of light. For this
reason, in the present embodiment, each secondary imaging lens is
constructed of a lens surface convex relative to the stop 33 and is
disposed in contact with the stop 33.
By appropriately setting each element in the optical path leading from the
two optical systems to the light receiving means as previously described,
it is possible to achieve the compactness of the entire device, contain
the device well in a limited space within a camera or the like and
increase the degree of freedom of assemblage.
On the other hand, FIG. 17 is an illustration depicting the secondary
imaging lens 34 from the front thereof. For example, let it be assumed
that as shown in FIG. 17, the vertex of the lens surface of one of eight
secondary imaging lenses, 34-3b, has been displaced leftwardly by a
distance d. Then, by this secondary imaging lens 34-3b, the projected
image of the field mask projected by the sensor 35 becomes such as shown
in FIG. 18. In FIG. 18, unlike FIG. 16, the projected image 36'-3b
corresponding to the secondary imaging lens 34-3b is displaced leftwardly
by a distance d'. Here, the relation between the distances d and d' can be
virtually expressed as:
d'=d.multidot.(1+.vertline..beta..vertline.),
where .beta. is the imaging magnification of the secondary imaging lens.
When such a state is brought about, the object side areas detected by the
sensors 35-3a and 35-3b will become different from each other and accurate
focus detection cannot be accomplished.
The ratio of the amount of out-of-focus of the objective lens to the amount
of image deviation on the two sensors differs depending on the imaging
magnification of the secondary imaging lens and the spacing between the
centers of the openings in the stop, and usually is of the order of
1:30-50. That is, this means that if the images on the two sensors deviate
from each other by 1 .mu.m, the focus position of the objective lens will
move by the order of 0.03-0.05 mm. Accordingly, if an attempt is made to
effect the focus detection of the objective lens with an error less than
0.03-0.05 mm also for a pattern such as a black and white edge inclined at
45.degree., the allowable deviation of the position of the vertex of the
secondary imaging lens will be 1 .mu.m even if it approximates to d--d',
and this is very severe.
When as shown in FIG. 2, the secondary imaging lens 34 is formed on the
surface of the prism member 49 to thereby make a unitary construction, if
these are formed of plastic, the vertex of the secondary imaging lens may
deviate greatly under the control of the complicated contraction of the
prism member which is large in volume and triangular in shape.
Further, if the prism member 49 is formed of plastic, it will be necessary
to take the expansion thereof caused by moisture absorption and a
variation in the refractive index thereof sufficiently into consideration,
and generally, a plastic material such as acryl readily absorbs moisture
and experiences expansion and a variation in the refractive index thereof.
Where the refractive index varies uniformly over the entire prism member,
the influence thereof is not so great, but if the distribution of the
refractive index occurs toward the interior of the prism member due to the
moisture absorption from the surface of the prism member, light rays
transmitted through the interior of the prism member will be bent and
accurate focus detection will become difficult. Particularly, in the case
of the prism member 49 which is large in volume, moisture absorption will
progress to the interior thereof and a long time will be required until a
balanced state is reached, and the influence thereof is very great.
Where focus detection is effected at a plurality of points in the
photographing range as described above, it is conceivable that the
accuracy of focus detection is affected by various causes.
In the example shown in FIG. 7A, the surface 34-4 of the secondary optical
system 34 which is adjacent to the light receiving means and the entrance
surface of the prism member 49 may be adhesively secured to each other at
a location 54, but alternatively, they may be disposed in opposed
relationship with each other with a slight gap therebetween.
However, if the exit surface of the secondary optical system 34 and the
entrance surface of the prism member 49 are adhesively secured to each
other, the reflection of the light on the surface of each member can be
decreased and the quantity of transmitted light can be increased, and also
the creation of the ghost light can be prevented, and this is preferable.
Also, in the present embodiment, the secondary optical system 34 is made
into a thin plate of good symmetry in shape, whereby the uniformity of
contraction during the molding of plastic can be improved and thus, there
can be obtained a molded article which is small in the deviation of the
vertex position of the lens surface of the secondary imaging lens.
Also, regarding the aforedescribed influence of moisture absorption, where
the secondary optical system 34 and the prism member 49 are separate
members as shown in the present embodiment, the secondary optical system
34 which suffers little from the influence of moisture absorption may be
formed, for example, of acryl which is great in moisture absorption but
good in moldability and heat resistance and the prism member which suffers
greatly from the influence of moisture absorption may be formed of
polycarbonate, polystyrene, MS resin or the like which is low in moisture
absorption, whereby it becomes possible to suppress the influence of
moisture absorption as a whole. Of course, preference may be given to the
utmost reduction in the influence of moisture absorption and the secondary
optical system may also be formed of one of these materials. Particularly,
polycarbonate and polystyrene are high in refractive index as compared
with acryl and are preferable plastic materials when the reflection by the
prism member is total reflection.
If the prism member 49 is formed of glass, it will be more effective in the
sense that the influence of moisture absorption is reduced. The prism
member is of a simple shape surrounded by flat surfaces and therefore can
be formed of glass relatively easily.
On the other hand, as shown in FIG. 7B, the secondary optical system 34'
and the prism member 49' may be formed of plastics or glasses differing in
Abbe number from each other, and may be cemented together with a curvature
given to the cemented surface 54' therebetween, as required, whereby the
elimination of chromatic aberration becomes possible.
Further, as shown in FIG. 7C, the secondary optical system 34 and the prism
member 49 may be cemented together with an infrared cut filter 54a of the
absorption type interposed therebetween. An infrared cut filter of the
absorption type, as compared with one of the evaporated type, is
characterized by inexpensiveness and low angle dependency of spectral
transmittance, but has a problem in environmental resistance and is
generally little used.
Particularly, it may be deteriorated in characteristics due to being
emulsified by moisture absorption, and it has been difficult for such a
filter to be used in cameras or the like which are used in severe
environments. However, if the infrared cut filter 54a of the absorption
type is interposed between the secondary optical system 34 and the prism
member 49 and the three are cemented together or an adhesive agent is also
applied to the end surfaces thereof to thereby shield the infrared cut
filter from the atmosphere, the problem of moisture absorption as noted
above will be solved and such a filter will become usable. The infrared
cut filter 44 of FIG. 1 should effectively be provided at a low position
so that the light from the photo-taking lens may not be reflected into the
film surface, and has required much space, but if an infrared cut filter
of the absorption type is inserted between the secondary optical system
and the prism member, the infrared cut filter 44 will become unnecessary,
and this will be very advantageous in making the focus detecting system
compact.
Turning back to the embodiment of FIG. 2, it has already been described
that the upper and lower openings 33-1a and 33-1b are larger in area than
the right and left openings 33-1c and 33-1d. If based on the concept that
the focus detecting system corresponding to the upper and lower openings
33-1a and 33-1b and the focus detecting system correspoding to the right
and left openings 33-1c and 33-1d are dealt with equally and the limits on
the low luminance side of an object to be photographed for which the two
focus detecting systems can operate are made equal, the central opening in
the stop 33 may be equally divided into four as shown, for example, in
FIG. 12.
In this case, however, as compared with the prior-art focus detecting
device as shown in FIG. 13 wherein there are only two openings in the
stop, the quantity of light entering the focus detecting system will
decrease to one half or less and focus detection will become impossible
for a dark object to be photographed or the accuracy of focus detection
will be reduced. When the object to be photographed is particularly dark,
it is necessary to operate an auxiliary illuminating system and project a
pattern onto the object to be photographed to secure brightness and
contrast, but again at this time, as compared with the prior-art focus
detecting device, a remarkable disadvantage is unavoidable with regard to
brightness.
In contrast, if use is made of the stop opening of the stop according to
the present invention as shown in FIG. 2, when the luminance of the object
to be photographed is low and an auxiliary illuminating system is used, a
reduction in the quantity of light is alleviated because the stop openings
33-1a and 33-1b of the focus detecting system which can more easily detect
the projected pattern of the auxiliary illuminating system as shown in
FIG. 9 are larger, and thus, it becomes possible to prevent the low
luminance limit from becoming extremely high. In FIG. 9, the portions
indicated by hatching are non-light-transmitting zones.
In the present embodiment, use is made of an example in which the projected
pattern of the auxiliary illuminating system is lateral stripes as shown
in FIG. 9, and this is because it is taken into consideration that the
projected pattern of the auxilairy illuminating system to be used in the
other two right and left marginal fields of view than the center of the
focus detecting device shown in FIG. 1 is similar lateral stripes.
That is, if the directions of change in the distributions of quantity of
light of the projected patterns of the auxiliary illuminating systems used
in three fields of view are the same, it will become possible to
illuminate the three fields of view at a time by projecting a pattern, and
this will become very advantageous in simplifying the construction of the
auxiliary illuminating system.
In the present invention, as regards the shape of the stop for making the
optical characteristics of the stop openings in the central portion of the
stop 33 different from each other, various modifications, in addition to
the shape shown in FIG. 2, are applicable.
FIGS. 8A, 8B and 8C show the shapes of the stop openings in the central
portion of the stop 33 according to the present invention.
In the embodiment shown in FIG. 8A, the central openings in the stop
correspond to the central openings in the stop of the FIG. 2 embodiment as
they are rotated by 90.degree., and are applied when the projected pattern
of the auxiliary illuminating system is vertical stripes as shown in FIG.
10. The projected pattern of the existing auxiliary illuminating system
incorporated in a stroboscopic lamp used in the conventional focus
detecting device as shown in FIG. 13 is often vertical stripes, and is
effective when it is usable and the conformability thereof to the
conventional system is to be maintained.
The feature of the embodiment of FIG. 8B is that among the four central
openings in the stop, the spacings a and b between the centers of the two
openings forming a pair are in the relation that a>b. The spacing between
the centers of the two openings forming a pair corresponds to the
so-called base line length in focus detection, and it is well known that
the longer it is, the higher becomes the accuracy of focus detection.
In the present embodiment, the base line length of the focus detecting
system which can more easily detect the projected pattern of the auxiliary
illuminating system is made greater, thereby preventing any reduction in
the accuracy of focus detection during the time of low contrast.
The feature of the embodiment of FIG. 8C is that the opening widths c and d
of the four openings in the stop in the direction of each field of view,
i.e., the direction in which the image deviates due to the focus state of
the objective lens, are in the relation that c<d. In other words, the
opening width in the direction of the field of view corresponds to the
F-number in the same direction, and in a range within which the influence
of diffraction can be neglected, the greater it is (the narrower the
opening width is), the higher becomes the contrast in the direction of the
field of view of the image formed on the sensor.
In the present embodiment, the F-number in the direction of the field of
view of the focus detecting system which can more easily detect the
projected pattern of the auxiliary illuminating system is made greater,
thereby preventing any reduction in the accuracy of focusing during the
time of low luminance and low contrast.
The stops of FIGS. 8B and 8C are ones for a case where the projected
pattern of the auxiliary illuminating system has a variation in quantity
of light chiefly in the vertical direction, but where said pattern has a
variation in quantity of light chiefly in the horizontal direction, the
stop openings may be rotated by 90.degree. and replaced with each other
just as in the relation between FIGS. 2 and 8A. Also, while in the
foregoing, the various elements regarding the stop openings such as area,
base line length and F-number have been described individually, two or
more of these may be made unequal to achieve the object of the present
invention.
According to the present invention, in a focus detecting device having a
plurality of focus detecting systems which share some of the fields of
view in the photographing range and effect focus detection with respect to
at least two directions which differ in the variation in the quantity of
light of an object to be photographed, the optical characteristics as a
stop such as the areas of the openings in the stop, the spacings between
the centers of the openings and the opening widths are made unequal,
whereby the rate of impossibility of focus detection for objects of low
luminance can be decreased and the reduction in the accuracy of focus
detection for objects of low luminance can be alleviated. Particularly,
when an auxiliary illuminating system is used, the conformability to the
projected pattern thereof is taken into consideration and therefore, there
can be achieved a focus detecting device capable of accomplishing good
focus detection even for objects at long distances.
Top